River and stream water quality and ecology - Greater Wellington ...

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River and stream water quality and ecology in the Wellington region: State and trends Appendix 2: River Environmental Classification (REC) As outlined in Section 2.1, rivers and streams in the Wellington region are diverse and some may have differing water quality simply due to their size, climate and underlying geology rather than due to human-induced impacts. To reduce this bias, comparisons between RSoE sites are undertaken using the River Environment Classification (REC). REC characterises river environments at six hierarchical levels, corresponding to a controlling environmental factor (Snelder et al. 2003). The factors, in order from the largest spatial scale to the smallest, are climate, source-of-flow, geology, landcover, network position and valley landform. The first four REC factors are explained in Table A2.1. See Appendix 1 for the REC description for each RSoE site. Table A2.1: REC classification levels, classes, mapping characteristics and criteria used to assign river segments to REC classes (after Snelder et al. 2003) Classification level and scale Climate (10 3 – 10 4 km 2 ) Source of flow (10 2 – 10 3 km 2 ) Geology (10 – 10 2 km 2 ) Landcover* (10 km 2 ) Classes and notation Warm extremely wet (WX) Warm wet (WW) Warm dry (WD) Cool extremely wet (CX) Cool wet (CW) Cool dry (DC) Mountain (M) Hill (H) Low elevation (L) Lake (Lk) Alluvium (Al) Hard sedimentary (HS) Soft sedimentary (SS) Volcanic basic (VB) Volcanic acidic (VA) Plutonic (Pl) Miscellaneous (M) Bare (B) Indigenous forest (IF) Pastoral (P) Tussock (T) Scrub (S) Exotic forest (EF) Wetland (W) Urban (U) Mapping characteristics Mean annual precipitation, mean annual potential evapotranspiration, mean annual temperature. Catchment rainfall volume in elevation categories, lake influence index. Proportions of each geological category in section catchment. Proportions of each landcover category in section catchment. Class assignment criteria Warm: mean annual temperature ≥ 12˚C Cool: mean annual temperature 500 mm and 50% annual precipitation volume >1,000 m ASL H: 50% precipitation volume 400 to 1,000 m ASL L: >50% rainfall 0.033 Class = spatially dominant geology category unless combined soft sedimentary geological categories exceed 25% of catchment area, in which case class = SS. Class = spatially dominant landcover category unless pastoral exceeds 25% of catchment area, in which case class = P, or unless urban exceeds 15% of catchment area, in which case class = U. * It is important to note that landcover types that are not classified as dominant using the REC criteria may still significant affect river and stream water quality and ecology. Further, in many cases, the current ‘condition’, as measured at each RSoE site, is the result of the cumulative impacts of all landcover types and associated activities in the upstream catchment. WGN_DOCS-#1100598-V3 PAGE 131 OF 160
River and stream water quality and ecology in the Wellington region: State and trends Appendix 3: Monitoring variables and methods Core variables Table A3.1 lists the core water quality and biological variables currently examined in the RSoE programme and provides a brief explanation of their relevance from a surface water quality perspective. Table A3.1: Key water quality and biological variables examined in the RSoE programme Variable Explanation/relevance Water temperature Indicator of biological activity – temperature affects the functioning of aquatic ecosystems and the physiology of biota, including cell function, enzyme activity, bacteriological reproduction rates, and plant growth rates. Requirement for aquatic life (eg, temperatures >19oC can stress trout). Influences dissolved oxygen concentrations (the higher the temperature, the lower the oxygen concentration) and can affect the toxicity of certain pollutants such as ammonia. Dissolved oxygen (DO) Essential for aquatic life – concentrations less than 5 mg/L adversely affect trout and concentrations of 2–3 mg/L may result in fish kills. Indicator of organic pollution (eg, sewage) – DO concentrations are reduced as bacteria require oxygen to break organic matter down. Indicator of photosynthesis (plant growth). pH Protection of aquatic life – particularly high (alkaline) or low (acidic) pH levels may adversely impact on aquatic biota. Alkaline conditions may also increase the toxicity of certain pollutants such as ammonia. Indicator of industrial discharges. Conductivity Indicator of total salts/mineral content – the lower the value, the purer the water is. Wastewater/effluents therefore have higher concentrations of minerals than natural water and a large increase in the conductivity in a water body can often be traced back to wastewater discharges. However, considerable natural variation exists and some rivers and streams may have naturally elevated conductivity concentrations. Visual clarity, turbidity and suspended solids Aesthetic appearance. Aquatic life protection – differences in water clarity affect the ability of sightfeeding predators (e.g., fish, birds) to locate prey and the ability of algae to photosynthesise and hence provide food for animals further up the food chain. Indicator of light availability for excessive plant growth. Indicator of catchment condition, land use. Suspended sediment in the water column can clog the gills of invertebrates and fish. Excessive deposition of sediment on the streambed can block and seal off interstitial spaces (the spaces between cobbles/stones where most fauna live or rest), reduce water flow to the hyporheic zone (water under the streambed) where some stream animals live, degrade fish spawning habitat and encourage the growth of nuisance aquatic plants. Total organic carbon Indicator of organic carbon content of a water body – provides a quick and convenient way of determining the degree of organic contamination (e.g., as a result of wastewater discharges). PAGE 132 OF 160 WGN_DOCS-#1100598-V3
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River and stream water quality and
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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5. Periphyton - state and trends 57
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Figure 2.1: RSoE monitoring sites a
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2.4.2 Biological variables River an
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4.2 Temporal trends River and strea
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TN (mg/L) Temperature ( 0 c) Shade
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Chlorophyll a (mg/m 2 ) 90 80 70 60
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25th percentile summer time flow m
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